Throughout his career, Marty Ralph has been an inspiration and leader—literally, an ambassador—bringing together scientists and decision makers-managers, researchers with local to regional interests, and federal science and academic research in order to mitigate real-world problems regarding extreme weather, flooding and droughts, and the management of crucial resources. Most visibly, Marty is known internationally for leading, community building, performing, and communicating groundbreaking regional to global research and applications of the new science of atmospheric rivers (ARs), which are long, narrow, moving corridors of near-surface atmospheric water vapor transport that when they encounter mountains, drop large amounts of rain and snow, resulting, e.g., in 80% of floods and 30%–50% of water resources in California. At the National Oceanic and Atmospheric Administration (NOAA) and, more recently, Scripps Institution of Oceanography, Marty has founded and led large research groups and collaboration networks. Meanwhile, he has become the world’s leading expert on ARs. For example, the AR literature has grown (since its beginnings in 1997) to receive >4,000 citations/year now, over a third of which are to work he authored or coauthored (Web of Science). After almost 15 years doing and then leading NOAA science, Marty founded the Center for Western Weather and Water Extremes (CW3E) at Scripps Institution of Oceanography in 2013 to advance AR science in whole new ways. Notably, Marty has never been satisfied for AR science to be "laboratory science." At CW3E, Marty has built major new programs and partnerships bridging research-to-application gaps. Two such applications are the following: (a) Forecast-Informed Reservoir Operations (FIRO)—During the 2012–2015 California drought, Marty organized a committee of scientists, engineers, and resource managers to model, assess, and essentially invent the options for safely incorporating modern AR forecasts into reservoir operations. Resulting FIRO applications on several California rivers now yield significant water supply improvements without major infrastructure investments. Currently, Marty leads FIRO assessments on seven more rivers, and with his guidance, the Corps of Engineers has embarked on triaging 700+ dams nationally for FIRO efficacy. (b) Atmospheric River Reconnaissance—Building on work he began at NOAA, Marty has more recently designed and negotiated annual, operational weather reconnaissance campaigns of wintertime air-, sea-, and land-targeted observations that are demonstrably and significantly improving U.S. storm forecasts. For these accomplishments and many more, Marty Ralph is already a recognized ambassador of AR science and its applications, with an impressive track record of enabling and implementing real-world societal benefits. Thus, Dr. Ralph very much exemplifies the AGU Ambassador Award. —Michael Dettinger, Scripps Institution of Oceanography, La Jolla, California